Measurement of cell-monolayer adhesion in cells transfected with N-CAM cDNAs

To measure the adhesion of cells expressing the neural cell adhesion molecule N-CAM, mouse Lmtk- fibroblast cells were transfected by a calcium phosphate precipitation technique with eucaryotic expression vectors encoding N-CAM polypeptides. We obtained cell lines expressing the 140-kDa transmembrane isoform of N-CAM at high levels by several rounds of selection by fluorescence-activated cell sorting and compared the adhesion of these cells to that of untransfected cells using a centrifugal removal assay that measures the centrifugal force required to remove radiolabeled probe cells from a cell monolayer. The adhesion of cells prepared from embryonic chicken neural retinas also was examined. Retinal probe cells remained associated with a retinal cell monolayer with an adhesive force of approximately 5 x 10(-6) dyn/cell, and this force was not reduced by treatment with specific anti-N-CAM antibody fragments. Transfected and untransfected mouse L cells each were dislodged from transfected cell monolayers with a removal force of 5 x 10(-5) dyn/cell and thus did not differ in their adhesion. These results support the hypothesis that N-CAM-mediated homophilic adhesion in retinal cells and transfected fibroblasts is relatively weak and that the major adhesive interaction involved in N-CAM-mediated cell-cell adhesion is heterophilic.